It is known that of all the daily activities performed by people major importance is attached to comfort during walking, which is greatly influenced by the type of shoe worn by the user; in particular such comfort in walking is determined by the degree of flexibility characteristic of the sole of the shoe, which flexibility should differ for different needs such as, for example, sporting activities which necessitate rigid soles to restore the necessary force of reaction, for example when jumping, or the normal gait of an elderly person who needs greater softness to cushion the rebound sustained by the foot with each step on the ground.
There are also known certain developments intended to provide a solution to this problem and based either on the use of different materials capable of imparting higher or lower rigidity to the sole, or on the use of insoles with air chambers of various designs.
Such air insoles include that of Patent EP O 293 034. Earlier air insoles, however, may pose major disadvantages on being applied to a shoe, either because of the difficulty of insertion therein during a normal industrial processing cycle, or because of the basic impracticability of achieving correct regulation of the pressure in the air chamber without rendering the insole uncomfortable because it is either too deflated, and therefore superfluous, or too inflated, resulting in the foot being supported on hard surfaces which soon cause aching feet and an awkward gait.